The invention relates generally to a one-component, moisture-curable adhesive composition with a plurality of spacer particles, and having controlled moisture vapor transmission and sound abatement properties. The adhesive composition is particularly suitable for adhesively bonding floor coverings to a variety of substrates.
A wide variety of flooring materials are available for use in residential and commercial applications. Wood floor coverings are a popular method of providing a decorative and long-lasting floor surface. However, the installation is typically a labor-intensive process that requires many steps to accomplish properly.
Wood floor coverings may be installed over a wide variety of substrates, including concrete, plywood, particle or chip board (underlayment grade), well-bonded vinyl and ceramic tile, cement backer board, gypsum patch/underlayments (dry, above grade), cement patch/underlayments, radiant-heat flooring, and terrazzo. When installed over concrete, these coverings are exposed to moisture vapor from beneath the concrete, as well as from the concrete itself. Moisture vapor acts according to the physical laws of gases and chemical equilibrium, and travels from one area to another whenever a difference of vapor pressure exists. In climate-controlled (air-conditioned) areas, such as residential dwellings, the ambient environment provides a condition where the air above a concrete substrate surface can readily absorb moisture from the earth, and therefore, tries to satisfy itself by constantly pulling moisture through the substrate, in an attempt to reach a rarely achievable condition of equilibrium.
If large enough, the moisture vapor driving force can cause the bottom of a wood floor covering adjacent to the concrete to expand (dimensional swelling caused by increasing moisture content) more than the top that is exposed to the climate-controlled environment. The end-result is called “cupping”, and provides an unsightly irregular appearance to the floor surface. Additionally, these dimensional changes in the wood floor covering can cause added stress to the adhesive bonds, which can also cause bond degradation and/or fracture. The cost to replace the damaged flooring can be expensive and time consuming.
A method to address the “cupping” problem is to provide sufficient drying time for the concrete substrate to achieve an acceptable level of vapor transmission to continue with the flooring installation. However providing sufficient drying time is not as widely followed because of the time limitations faced by installers. Another method is to seal the surface of the concrete with impervious paper or plastic sheets, or to apply a membrane-forming curing compound to serve as a vapor bather or retarder. This membrane must be a continuous layer of substantially uniform thickness, since any imperfections can provide pathways for which moisture vapor can pass. Commonly known membrane-forming curing compounds are two-part epoxy-based or water-based sealers. These sealers require premixing before application, which can result in improper mixing of the components, and therefore, job failures, or require up to several days of curing before the sealer is fit for application. Single component moisture-curing polyurethanes are another commonly used sealer, and can require cure times of half a day or more, depending on ambient conditions.
Additional information relevant to attempts to address these “cupping” problems can be found in U.S. Patent Application Publication 2009/0044364 and 2010/0059164, and in International Patent Application Publication WO 2008/145458. However, each one of these references suffers from one or more of the following disadvantages: poor adhesive flow characteristics that result in a non-uniform adhesive film thickness or less than 100% adhesive coverage on the underside of the floor covering when the flooring covering is installed; air gaps in the adhesive layer created by spacer particles in the adhesive composition, thereby creating a non-continuous film which allows for increased moisture vapor transmission; poor moisture vapor transmission control due to polymer and/or additive technology of the adhesive composition; use of specialized tools for adhesive application that need to be frequently replaced due to wear, resulting in inconsistent, non-uniform adhesive membrane thickness as the installation progresses; and, inability to regulate adhesive film thickness and prevent adhesive “squeeze out” if too much pressure is applied to the top of the floor covering during installation.
For the foregoing reasons, there exists a need for an adhesive composition that can serve the purpose of an adhesive and moisture vapor barrier with a single application of material that overcomes the shortcomings of the available products and methods.